1. Field of the Invention
The present invention relates to a method for detecting and analyzing a trace substance by utilizing the agglutination assay, in which an analyte reacts with a particle-labeled anti-analyte, such as an antibody, to cause the particle agglutination. Particularly, the present invention relates to a dry analysis method for determining an analyte, which comprises bringing a solation agent into contact with a medium of a non-fluid substance to increase the fluidity of the medium, thereby causing the agglutination of the particles bearing the anti-analyte in the medium. Also, the present invention relates to a dry analysis element which enables such analysis method.
2. Description of the Related Art
In recent years, it has come to be very important to quantitatively analyze a trace substance, particularly antibody or antigen, in a specimen promptly, conveniently and precisely in order to diagnose the condition of diseases or judge the effects of treatment. For this purpose, widely employed has been an immuno-serological test for assaying the existence of an antigen or antibody in the body fluid, in which the antibody or antigen is adsorbed and immobilized to insoluble carrier particles and the resulting particles is reacted with the antigen or antibody.
The latex particles agglutination immunoassay is performed routinely by mixing a suspension of antibody-coated latex particles (sensitized latex) with a specimen on a glass plate. The latex particles agglutinate, or fail to agglutinate, as a result of interacting with the analyte antigen in the specimen. The extent of the agglutination can be determined by visual inspection. This assay makes it possible to semi-quantitatively analyze the antigen in the specimen by diluting the specimen at various ratios similar to another qualitative assay.
In Japanese Patent Publication Nos. 11575/1983, 43138/1987 and 55013/1987, there is proposed a method, in which latex particles having an antibody bound thereto is reacted with the antigen in the sample and the amount of the agglutination of the latex particles is determined optically by nephelometry. According to the proposed method, an antigen or antibody has come to be analyzed quantitatively by an automatic analyzer.
In addition, Unexamined Japanese Patent Publication (KOKAI) Nos. 141665/1990 and 209879/1993 disclose a method wherein an antigenic substance is detected by measuring a change in the absorbance upon the agglutination of the colloidal gold-labeled antibodies.
The above-described immunoassays do not need B/F separation and in this point, they are useful. The latex reagent is, however, poor in storage stability, since it is in the liquid form. In the colloidal gold agglutination, the colloidal gold solution or dispersion is not suitable as a reagent because of poor storage stability. A colloidal gold-labeled reagent in the lyophilized form must be mixed with a dedicated solution upon measurement, which makes the operation cumbersome. This method is also accompanied with such a drawback as unsuitability for use in the measurement of a small amount of a sample.
A so-called dry analysis method is, on the other hand, superior in storage stability and convenient operation. The so-called wet system (or solution system) comprises dissolving a reagent to be used for the assay in an aqueous solvent, thereby preparing the corresponding reagent solution, adding this reagent solution to a sample to be analyzed and then measuring the color reaction product by a calorimeter, while the dry analysis method comprises spotting an aqueous sample directly to a dry analysis element, such as test piece, analytical slide or analytical tape, having a reagent composition incorporated therein in the dry form and effecting colorimetry of the color development or color change occurring in the element. The dry system is superior to the wet system using a reagent solution in convenient operation and speedy assay.
A method for causing agglutination in the layer of a dry analysis element, thereby directly detecting the existence of an agglutinate itself in the layer construction has not yet been proposed. It can adopt the agglutination in a gel state, like as the Ouchterlony technique, which involving immunoprecipitation through an agar gel. Ouchterlony test is one of immunodiffusion methods, in which an antigen and an antiserum diffuse in the agar gel from each of two holes made in the gel plate. The antigen and the antiserum meet each other to form a visible precipitation line. Long time duration is necessary for the test, since the diffusion lasts for some time.
In order to cause agglutination of the labeling carrier in a gel medium in short time, the gel which is to be a place for reaction is required to have fluidity sufficient for causing agglutination. If sufficient humidity is required for maintaining this fluidity, such an analysis element cannot be classified as an element stored in a dry condition (or semi-dry condition). Moreover, when the gel has high fluidity, it needs a special care for packaging or storage, which makes this method far from convenience.